Numerous hydraulic mechanisms comprise a casing which defines an enclosure capable of containing a hydraulic fluid, but which, initially, at the moment of assembly, contains air which must be evacuated before the mechanism is first put into operation. This is usually effected by providing a plurality of vent screws so that, whatever the assembly of fit of the mechanism on the receiving structure, at least one vent screw will be in operational position. Each vent screw is expensive and the large number of such screws contributes to increasing the manufacturing cost of the mechanisms.
It is an object of the invention to propose a novel arrangement which, by eliminating the special vent screws, overcomes the drawback set forth hereinabove.